In instant photography, an image is formed by development processing with an alkaline processing solution within a film unit and, after the elapse of a prescribed time, the alkaline processing solution is neutralized to stop development and stabilize the image. The neutralization mechanism is usually composed of a neutralizing layer and a neutralization timing layer and mostly provided in a cover sheet in cases of monosheet type instant light-sensitive materials or in an image-receiving sheet in cases of peel-apart type instant light-sensitive materials. The neutralizing layer and the neutralization timing layer are formed adjacent to each other, and a hydrophilic organic colloidal layer (image-receiving layer) is further provided adjacent to the neutralization timing layer in the case where the neutralization mechanism is provided in an image-receiving sheet. In many cases, each of these layers differs in material from each other so that the conventional multi-layer neutralization elements show poor adhesion between layers in a dry state or wet state. This poor adhesion causes various unfavorable disorders before, during and after processing, such that the above-described layers are separated at the time of finishing instant film units; and peel-apart type instant materials suffer separation between these layers upon peeling of a light-sensitive element and an image-receiving element after development processing, which results in a part of the light-sensitive element remaining on the image-receiving element, or a part of the image-receiving element remaining on the light-sensitive element. Further, when an adhesive tape, e.g., Cello-Tape, is once attached to an image-receiving element of the peel-apart type instant film after having been processed to fix it on a mount of an album or a wall and then removed therefrom, the surface layer of the image-receiving element is separated off together with the adhesive tape to cause disappearance of a part or the whole of an image. Furthermore, when water attached on a processed image-receiving element is wiped away, the layers are separated, and loose a part or the whole of an image.
In order to improve such poor adhesion between layers, it has been proposed to interpose a primer layer between layers having poor adhesion, as disclosed in U.S. Pat. Nos. 4,297,432 and 4,297,195, European Pat. Nos. 46,692A2, 45,693A2, and 45,694A2 and U.S. Pat. No. 4,298,682, etc. However, since the proposed primer layer comprises a mixture of two or more copolymers having relatively complicated structures, preparation of these materials is complicated and also entails high cost.